FIG. 18 is a diagram for illustrating an inverter circuit disclosed in JP-A-10-075581. The inverter circuit generates a predetermined alternating current voltage using the voltage of an alternating current power source and a direct current power source voltage obtained by temporarily converting the voltage of the alternating current power source into direct current voltage.
In the diagram, 1 is a single phase alternating current power source, 2 is a capacitor, 3 is a converter circuit, 4 is an inverter circuit, 5 is a filter circuit, and 6 is a load.
The single phase alternating current power source 1 has a terminal R and a terminal S, wherein an alternating current voltage is output between the terminal R and terminal S. The capacitor 2 is connected between the terminal R and terminal S of the single phase alternating current power source 1.
The converter circuit 3 has as main components a series circuit of capacitors Cp and Cn, a series circuit of switching elements Qp and Qn, and a reactor L. The series circuit of the capacitors Cp and Cn is connected between a positive side direct current terminal P and negative side direct current terminal N of the converter circuit 3. Also, a series connection point of the capacitors Cp and Cn is connected to a neutral terminal O of the converter circuit 3, and is connected to the terminal S of the single phase alternating current power source 1. The series circuit of the switching elements Qp and Qn is connected in parallel to the series circuit of the capacitors Cp and Cn. The reactor L is connected between the terminal R of the single phase alternating current power source 1 and a series connection point of the switching elements Qp and Qn.
The inverter circuit 4 has as main components a series circuit of switching elements Q1 and Q2 and a bidirectional switch element S1. The series circuit of the switching elements Q1 and Q2 is connected between the terminal P and terminal N of the converter circuit 3. A series connection point of the switching elements Q1 and Q2 is connected to an alternating current output terminal U of the inverter circuit 4. An alternating current output terminal V of the inverter circuit 4 is connected to the neutral terminal O of the converter circuit 3. The bidirectional switch element S1 is connected between the alternating current output terminal U of the inverter circuit 4 and the terminal R of the single phase alternating current power source 1.
The alternating current output terminals U and V of the inverter circuit 4 are connected to the filter circuit 5. The filter circuit 5 is a circuit wherein a reactor Lf1 and a capacitor Cf1 are connected in series. The load 6 is connected to both ends of the capacitor Cf1.
The heretofore described configuration is such that the converter circuit 3 causes the switching elements Qp and Qn to turn on and off alternately, thereby charging the capacitors Cp and Cn to a predetermined voltage. The value of the voltage with which the capacitors Cp and Cn are charged is higher than the amplitude value of the voltage of the single phase alternating current power source 1.
The inverter circuit 4 is such that an operation whereby any two elements of the switching elements Q1 and Q2 and bidirectional switch element S1 are turned on and off is carried out, thereby outputting an alternating current voltage having a predetermined fundamental wave element between the alternating current output terminals U and V.
The voltage output between the alternating current output terminals U and V is applied to the load 6 after a high frequency element is eliminated in the filter circuit 5.
Further, when a voltage higher than the voltage of the single phase alternating current power source 1 is output, the inverter circuit 4 is such that, when the voltage of the single phase alternating current power source 1 is of a positive half-cycle, the switching element Q1 and bidirectional switch element S1 are alternately turned on and off. At this time, the switching element Q2 is in an off-state. Meanwhile, when the voltage of the single phase alternating current power source 1 is of a negative half-cycle, the inverter circuit 4 is such that the switching element Q2 and bidirectional switch element S1 are alternately turned on and off. At this time, the switching element Q1 is in an off-state.
Also, when a voltage lower than the voltage of the single phase alternating current power source 1 is output, the inverter circuit 4 is such that, when the voltage of the single phase alternating current power source 1 is of a positive half-cycle, the switching element Q2 and bidirectional switch element S1 are alternately turned on and off. At this time, the switching element Q1 is in an off-state. Meanwhile, when the voltage of the single phase alternating current power source 1 is of a negative half-cycle, the inverter circuit 4 is such that the switching element Q1 and bidirectional switch element S1 are alternately turned on and off. At this time, the switching element Q2 is in an off-state.